Is contraction joint of slab a concrete shear failure and only dowel action of rebar

[AskTooMuch]

Is contraction joint of a slab a concrete shear failure and only the dowel action of rebar resist shear?

I'm looking at some drawings and an engineer put contraction joint on an elevated slab. This has been constructed a long time ago. I'm wondering about the shear capacity of this elebvated slab with contraction joint.

 

[r13]

Is this contraction joint near any support? Need more details, a floor plan will be helpful.

 

[KootK]

Is contraction joint of a slab a concrete shear failure and only the dowel action of rebar resist shear?

I wouldn't call it a failure so much as a special condition where diagonal tension isn't the only mode of shear failure to be checked. In modern ACI lingo, we'd also check the vertical plane formed by the joint using ACI's shear friction provision. Depending on how smoothly the joint was constructed, that may or may not be primarily dowel action. Often there will be aspects of the joint construction that reduce the reliance on dowel action: keyways, back slopped joints, edge formers specifically designed to create a rough surface... stuff like that.

 

[r13]

Depending on how the reinforcing steel is placed, a contraction joint can mean for different purpose - crack control, or to accommodate contraction/expansion produced movement/stress. In general, the bars across the plane need to pick up the gravity load without the help from the concrete. At the interface, the connectivity of the concrete on each side can either be treated as in pin-pin condition (an internal hinge), or a roller on the tip of a cantilever.

 

[hokie66]

Movement joints take various forms. If a plan and joint detail can be provided, we may be able to give you an informed opinion.